The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-medium noise ratio (SMNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium, and by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high-density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SMNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is also recognized that underlayers having a fine grain structure are highly desirable, particular for growing fine grains of hexagonal close packed (HCP) Co-alloys deposited thereon.
Previous attempts to improve the SMNR and coercive force with increasing areal density have used ex situ post-deposition annealing of the magnetic thin film to reduce anisotropy without increasing grain size. Such attempts have met with limited success in providing a suitable product with increased coercivity, however, due to the introduction of environmental contaminants and the need to expose the thin film to high temperatures over a relatively long period of time to achieve satisfactory results. The annealing conditions employed have subjected the thin film to oxygen and, thereby, required the use of thick caplayers. The thick caplayers of the prior art result in unacceptable head-to-media spacing that can interfere with the operation of devices employing this type of recording media such as hard disk drives.
In U.S. Pat. No. 5,989,728 to Coffey et al., an ex situ post-deposition annealing process is described in which a CoPt thin film of 25 nm to 200 nm is annealed at 550° C. to 750° C. for approximately 10 minutes. Coffey states that it is preferable, however, to anneal the thin film at 650° C. to 700° C. Further, the annealing process of Coffey requires the use of a quartz lamp furnace with flowing Ar/4% H2 gas to prevent oxidation.
In U.S. Pat. No. 6,117,282 to Kuo et al., a method for producing a Magnetic recording medium thin film is described wherein the CoTb magnetic layer is protected by a SiNx layer having a thickness of approximately 10 nm and annealed at 250° C. for approximately 60 minutes in a vacuum furnace. Kuo et al. do not describe the signal characteristics or SMNR of their described recording media. The major disadvantages of the Kuo process are the following. First, annealing is performed in a vacuum furnace, which is ex situ from the sputtering chamber in which the SiNx layer was deposited. When annealing is performed ex situ, it is intractable to prevent oxygen from entering the magnetic layer, thus deteriorating the performance of the recording media. Second, the large energy requirement to maintain the annealing temperature for a long period of time, greatly increasing the cost of the recording medium.
It would therefore be desirable to have a magnetic recording medium with a minimal Cr content that exhibits high coercivity and a high signal to medium noise ratio.
It would also be advantageous to have a method of producing a recording medium that provides a magnetic recording medium with a high linear recording density, high signal to noise ratio, and high coercivity that can be integrated into current manufacturing processes economically and efficiently where the recording medium does not need to be exposed to high energy sources for long periods of time or removed or subjected to multiple manufacturing process such as the ex situ annealing process of Coffey.
In short, there exists a need for a process if manufacturing a magnetic recording medium in accordance with the criteria stated above that does not achieve increased coercivity through grain coarsening or increasing Cr content.